November 10, 2009

Common variant for straight hair in Europeans

American Journal of Human Genetics doi:10.1016/j.ajhg.2009.10.009

Common Variants in the Trichohyalin Gene Are Associated with Straight Hair in Europeans

Sarah E. Medland et al.

Abstract

Hair morphology is highly differentiated between populations and among people of European ancestry. Whereas hair morphology in East Asian populations has been studied extensively, relatively little is known about the genetics of this trait in Europeans. We performed a genome-wide association scan for hair morphology (straight, wavy, curly) in three Australian samples of European descent. All three samples showed evidence of association implicating the Trichohyalin gene (TCHH), which is expressed in the developing inner root sheath of the hair follicle, and explaining ∼6% of variance (p = 1.5 × 10−31). These variants are at their highest frequency in Northern Europeans, paralleling the distribution of the straight-hair EDAR variant in Asian populations.

"All three samples showed evidence of association implicating the Trichohyalin gene (TCHH), which is expressed in the developing inner root sheath of the hair follicle, and explaining ∼6% of variance (p = 1.5 × 10−31). These variants are at their highest frequency in Northern Europeans, paralleling the distribution of the straight-hair EDAR variant in Asian populations."

- I read it as two independent mutations. The only thing that is similar is the distribution, I conjecture in northernmost regions.

"All three samples showed evidence of association implicating the Trichohyalin gene (TCHH), which is expressed in the developing inner root sheath of the hair follicle, and explaining ∼6% of variance".

The way I read it is that all three groups (straight, wavy, curly) had the same gene. Variations in the gene accounted for just 6% of the diversity. If all phenotypes have the same gene that gene can hardly be responsible for the different groups. A switching on or off gene is involved. What is it, and where did it come from? And what selection pressure could be responsible for the development of straight hair in colder regions, such as East Asia and Northern Europe?

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